Thermal Anomalies Trigger Widespread Coral Bleaching in Djibouti in 2023: A Scientific Assessment from the Gulf of Aden (Indian Ocean)

Coral reefs in Djibouti, located at the biogeographic junction of the Red Sea and the Indian Ocean, remain among the least studied in the region despite increasing climate-driven pressures. This study provides the first scientific documentation of a large-scale bleaching event in Djibouti following the extreme thermal anomaly of 2023. Benthic surveys conducted across 16 sites in Moucha–Maskali Islands, Arta, Tadjourah, and Obock revealed bleaching at all sites, with the highest levels recorded at Ras Bir (23.4%) and Sable Blanc (24.1%), predominantly affecting thermally susceptible such as Acropora and Pocillopora. More thermally tolerant massive corals, particularly Porites, Favia, and Platygyra, exhibited limited bleaching and dominated healthier sites such as Arta. Satellite-derived sea surface temperature (SST) and Degree Heating Week (DHW) data confirmed record-breaking heat stress in 2023, with SST peaking at 35.2 °C and DHW reaching 13.87 °C·week−1—the highest recorded. The pronounced spatial variability in bleaching reflects the combined influence of thermal stress, sedimentation, water quality, and reef geomorphology. Although mortality remained moderate, the findings indicate rising vulnerability of Djibouti’s reefs and underscore the urgent need for continuous monitoring, targeted management interventions, and mitigation of local stressors to enhance resilience in the region.